Disease prevention begins with immunization

Your immune system is a complex group of cells, tissues and organs working together to protect your body from harmful disease-causing microbes, such as bacteria, and viruses, which may cause an infection. When functioning properly, your immune system prevents these microbes from entering your body. When a microbe does enter your body, your immune system will respond by launching an attack against the microbe to destroy it before it causes an infection.
Immunization is one way to help protect your body against a disease. This process begins with vaccination, or when a vaccine is injected into the body to provide immunity from a specific disease. The vaccine itself contains killed or modified microbes, or parts of microbes, which trigger a reaction alerting the immune system that an infection has occurred, even though there is no actual infection present. The immune system then attacks the vaccine, creating antibodies against the microbe contained in the vaccine. These antibodies allow the body to build immunity against the microbe. If your body is exposed to the microbe again in the future, your immune system will quickly recognize it and take steps to prevent an infection.
When you are born, your body has protection from certain diseases thanks to antibodies you receive from your mother. Unfortunately, this protection is only temporary. That’s why pediatricians recommend infants and children receive various vaccinations throughout childhood (click on the chart below for more details). New parents should be sure to talk with their child’s pediatrician about the appropriate vaccination schedule and discuss any questions or concerns about vaccines.
As an adult, it is important to remember the role vaccinations continue to play in keeping you healthy. For example, all adults, age 18 and older, are encouraged to get the flu vaccine each year to protect against the seasonal flu. It is especially important to get the vaccine if you, someone you live with, or someone you care for, has a higher risk of complications from the flu. People at higher risk include infants and children, pregnant women and the elderly.
Additional vaccines are also encouraged for adults, including the Tetanus-diphtheria vaccine, which adults should receive every 10 years. Adults should also receive the one-time vaccine for shingles (caused by the same virus that gave you chickenpox as a child) after age 60. The first dose of the pneumococcal vaccine should be administered at age 65, with a second dose 6-12 months later. If you have specific questions about what vaccinations are best for you, talk with your doctor.
Sources:
http://www.vaccines.gov/basics/
http://www.cdc.gov/vaccines/vac-gen/imz-basics.htm
http://kidshealth.org/parent/general/body/vaccine.html
http://www.nlm.nih.gov/medlineplus/immunization.html